1. Field of the Invention
The present invention relates to a technology of smoothing dispositions of lattice points for the purpose of creation of a profile.
2. Description of the Related Art
Image equipment such as a display or a printer supports color image data each of whose pixels signifies a color by representing shades of color components on respective gray scales. For example, colors are defined in any of various color spaces including an RGB color space defining three colors of red, green, and blue and a CMY color space defining cyan, magenta, and yellow (including light cyan, light magenta, dark yellow, and black). The definitions of colors are used as color image data. The colors are generally dependent on or inherent to image equipment. A color correction lookup table specifying the relationships of correspondences between sets of colors supported by one piece of equipment and sets of colors supported by another piece of equipment is employed so that the same image can be outputted in the same colors among various pieces of image equipment.
Because of a restricted storage capacity and the workability in creating the color correction lookup table, it is unfeasible to create the color correction lookup table that specifies the relationships of correspondences of all sets of colors supported by one piece of image equipment with those supported by another piece of image equipment. Normally, the relationships of correspondences of a specific number of typical colors supported by one piece of image equipment with those supported by another piece of image equipment are specified in the color correction lookup table. The relationships of correspondences of the other colors are calculated through interpolation. Namely, colorimetry is not performed on numerous colors but is performed on a measurable number of colors generated from image equipment. The color correction lookup table thus specifies the relationships of correspondences of a specific number of typical colors.
Precision in interpolation depends on the dispositions of lattice points that are defined in a color space in order to represent typical colors specified in a color correction lookup table. Namely, data items to be represented by a lattice point are interpolated using data items represented by lattice points adjoining the lattice point that is an object of interpolation. Unless lattice points are disposed smoothly, the precision in interpolation is degraded. This raises the possibility that a tone jump or a color twist may occur. A technology for smoothing the dispositions of lattice points has been known (refer to, for example, Japanese Unexamined Patent Publication No. 2003-116012). Namely, conventionally, the relationships of a certain lattice point to its surrounding lattice points are smoothed using a three-dimensional filter in order to determine the positions of lattice points in an RGB or CMY color space.
The conventional smoothing has difficulty in maintaining a color gamut over a period before or after smoothing is performed, or in determining smooth lattice points as a whole while confining a specific lattice point to a specific position. Specifically, when a color correction lookup table is created, while lattice points that are located on the boundary of a color gamut are held intact, other lattice points must be smoothly disposed in order to define as large a color gamut as possible. Moreover, when gray or any other specific color is maintained, while lattice points are disposed along an axis signifying gray, surrounding lattice points must be smoothly disposed in relation to the lattice points disposed on the gray axis. However, even when a weighted mean is calculated according to whether smoothing is performed or not in the same manner as it is in the related art, the weighted mean does not always relate to an ideal position. Lattice points cannot be smoothly disposed while various conditions are satisfied, that is, while a color gamut is held intact and a desired lattice point is fixed to a position at which the lattice point signifies a desired color.